The analysis of PAR-3 in flow-mediated endothelial planar cell polarity

• Applicant: Dr. Masanori Nakayama
• Subject Area: Cell Biology
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 329963658

The vasculature expands substantially during development with blood flow. Expansion of existing vasculature, termed angiogenesis, must tightly coordinate a complex series of steps. Previous works, including my findings, have revealed the molecular basis of this process. Key regulators of blood vessel function are Vascular Endothelial Growth Factor and its tyrosine kinase receptors, VEGFRs. I have shown that ephrin-B2 forms a protein complex with Partitioning defective 3 (PAR-3) and atypical PKC (aPKC), controlling VEGFR signaling. While coordinated motile and proliferative behavior of ECs are crucial for angiogenesis, the fundamental function of ECs is to establish a barrier between the blood and the rest of the body. ECs show profound morphological adaptation to hemodynamic shear stress. ECs have three different cellular polarities; sprouting ECs have front-rear polarity, and established endothelial tubes have apical-basal polarity and planar cell polarity (PCP) parallel to blood flow. Thus, polarity switching and maintenance are a key feature of this process. A growing body of evidence is accumulating to show that PAR-3 and aPKC are crucial for controlling cell polarity across many cell types and animal species. However, the role of PAR-3 and aPKC in endothelial polarity during angiogenesis and blood vessel homeostasis remains elusive. In light of these observations, we have addressed the role of PAR-3 in endothelial polarity in physiological and pathological conditions. We have already examined the effect of EC specific gene inactivation of PAR-3. Our preliminary data have shown that PAR-3 controls EC Golgi orientation and thereby endothelial PCP under flow in vitro and in vivo. Furthermore, we found that GSK3beta activity was controlled by flow, which was impaired by PAR-3 knockdown in vitro. Moreover, inflammatory response examined by VCAM1 expression was upregulated in PAR-3 KD cultured ECs and EC specific KO mice.It is well appreciated that regions of disrupted flow in the aorta often show disorganized Golgi orientation. Clinical observations indicate that shear stress on the blood vessel wall contributes to the site specificity of vessel pathogenesis such as atherosclerosis lesion. However, a causative association between endothelial PCP and vascular disease progression has not yet been shown. It is unclear whether disrupted PCP in ECs is a consequence or causation of disease progression. The goal of proposed study is to clarify this important issue. The sum of the planned work will provide substantial new insights into endothelial polarity formation and homeostasis in vivo. Given the important function of the vasculature, understanding the contribution of EC PCP to pathogenesis will yield novel insights into fundamental biological mechanisms and is likely to open up new exciting opportunities for future drug development. This may well lead to the development of new therapeutic strategies for the treatment of pathologies.

• DFG Programme: Research Grants